Materials with fine-scale microstructures have long been recognized to exhibit remarkable and technologically attractive properties. In the past decade, interest has been growing in a new class of materials that are composed of ultrafine grains or particles. A feature of such "nanostructured" materials (n-materials) is the high fraction of atoms that reside at the grain boundaries or interfaces in the materials which exerts a profound influence on properties. Although much of today's research activity in the n-materials field is focused on the preparation of n-powders and their consolidation into bulk parts, there is growing interest in the fabrication of coatings and free-standing forms. Furthermore, there is an urgent need to develop scalable processes for the economical production of all types of nanostructured materials. The present invention addresses this need.
Nanophase powders have been produced in experimental quantities for almost a decade. The prior art methods of producing nanophase powders, however, are limited in the capability to produce commercial quantities of powders. The production of commercial quantities of mixed element technically important refractory compounds such as SiC, WC, HfC, Si.sub.3 N.sub.4, ZrO.sub.2 and A1.sub.2 O.sub.3 and many other similar compounds has been especially difficult. Commercial quantities of these mixed element refractory nanophase powders have been produced by the thermal decomposition metalorganic precursors in either a combustion flame or plasma flame at ambient or near-ambient pressures. Production of nanophase powders by the combustion flame and plasma flame methods, however, have had the disadvantage of producing agglomerated powders. This agglomeration of nanophase particles is problematic in the fabrication of monolithic ceramic shapes for structural applications, where the bridging of agglomerated particles causes residual porosity in the sintered material, seriously limiting performance. The present invention overcomes the disadvantages of the prior art nanophase particle synthesis processes by providing a method for producing commercial quantities of mixed element nanophase ceramic powders without the presence of particle agglomerates through the controlled thermal decomposition of the metalorganic precursors in a low pressure environment.